Conventionally, as a method for noninvasively and successively performing the determination of the boundary of a living tissue or a blood vessel wall, the measurement of a value of a blood vessel inner diameter, the measurement of an IMT value, or the like by using an ultrasonic diagnostic apparatus, it has been known to use a luminance signal of image data for measurement, to obtain an IMT value (see, for example, JP 2000-271117 A (page 3, FIG. 1) and Japanese Patent No. 2889568 B (page 5, FIG. 8)), or the like based on a standard structure of a living tissue or a blood vessel wall. However, there has been no discussion in the prior art for displaying a body tissue moving in accordance with a body motion, as if it were standing still, or a prior art for using the quasi-still information for structural analysis of the body tissue, and thus no prior art document is referred to.
In the above-mentioned prior art, in order to extract the boundary of a living tissue, it is necessary to obtain a still image in which a random noise component is suppressed to a certain level or lower. However, in the case where the living tissue as a target moves in accordance with a body motion or the like, when a general noise filter for images is used to remove a random noise component, a living tissue component as a target of image analysis also is influenced by the noise filter. As a result, a contour is displayed with degraded sharpness and the like, making it difficult to perform precise structural analysis of a living tissue.
In particular, in an actual medical diagnosis of a carotid artery, there is the following problem. That is, since luminance information of image data is used for structural analysis of a target blood vessel wall, there is little difference in luminance between a random noise component and a signal corresponding to a tunica intima tissue in a living body having low tunica intima luminance or the like. Accordingly, it is impossible to perform precise structural analysis of a living tissue stably and easily.